1. Field of the Invention
The present invention relates to a drum cleaning blade for an electrophotographic copying machine. In a transfer type of the electrophotographic copying machine, there is in general employed a rotatable drum provided with a photoconductive light sensitive layer on the cylindrical outer surface therof in which an electrostatic latent image is formed. The latent image is then developed to a toner image which is in turn transferred to a transfer sheet to be recorded. After the image transfer, it is generally required to remove the toner paricles from the durm surface.
To this end, the electrophotographic copying machine has a drum cleaning apparatus which includes a drum cleaning blade often referred to as the doctor blade.
The present invention relates to such doctor blade (hereinafter referred to simply as blade).
2. Description of the Prior Art
A schematic view of a fundamental arrangement of a hitherto known drum cleaning apparatus is shown in FIG. 1. A drum 1 having a circumferential photo-conductive layer is rotated in the direction indicated by an arrow.
A blade 2 is held at a preselected fixed position in an inclined state by a holder 4 so that the lower edge of the blade 2 bears on the outer surface of the cylindrical drum against the rotating direction thereof.
The blade 2 is formed of a sheet material having resiliency and has the contacting lower edge in a straight configuration so as to assure a uniform contact with the cylindrical outer surface of the drum 1. The toner particles deposited on the drum surface are scraped off, as the lower edge of the blade 2 is in slidable engagement relative to the outer cylindrical surface of the drum 1.
Reference numeral 5 denotes a guide plate for collecting the toner particles, which is disposed in an inclined state with the upper edge thereof bearing on the outer cylindrical surface of the drum at a position below and upstream of the blade 2 as viewed in the rotating direction indicated by an arrow.
The toner particles as scraped off by the blade 2 will slide down along the drum surface onto the guide plate or chute 5, whereby the toner particles are introduced into a collecting container (not shown) having an inlet opening receiving therein the lower edge of the guide plate 5.
In the drum cleaning apparatus having the scraping blade 2 as described above, the toner particles will be scattered laterally and fall from the both sides of the drum 1 and/or guide plate 5. Such undesirable phenomenon will become more remarkable in the case in which feeble transverse vibrations are applied to the scraping blade with a view to enhancing the scraping efficiency.
As an attempt to dispose of the difficulty described above, it has been heretofore known and also widely adopted that side portions of the drum 1 are stretched outwardly beyond the side edges of the blade 2.
However, in order that such arrangement is to be practically effective, the lateral exension d of the drum 1 will amount to 30 to 40 mm, when the side edge of the guide of the guide plate 5 is extended for 5 mm laterally from the adjacent side edge of the blade 2.
As a result, the overall length of the drum 1 has to be longer than that of the blade 2 by 60 to 80 mm.
Consequently, the drum which is inherently to serve as the carrier for the photo-sensitive layer for producing an electrostatic latent image to be developed by the toner particles must have relatively large side portions which play no part as the carrier for the photo-sensitive layer, while the opening of the toner collecting container has to be of correspondingly increased size, involving high costs of the copying machine as well as an enlarged structure thereof, against a prevailing demand for miniaturization.
As an approach for eliminating the difficulty described above, it has been also heretofore known that a circumferential groove 6 is formed at each side of the drum, while the blade 2 is provided with projections 7 at both sides each of which is adapted to be slidably fitted in the associated groove 6. With this arrangement, it is necessary to hold the blade 2 in a strictly defined position relative to the rotating drum 1, involving increased manufacturing costs, notwithstanding the impossibility of attaining the miniaturization desired.